Illumination system particularly for microlithography

ABSTRACT

There is provided an illumination system, particularly for microlithography with wavelengths≦193 nm. The illumination system includes a primary light source, a first optical component, a second optical component, an image plane, and an exit pupil. The first optical component transforms the primary light source into a plurality of secondary light sources that are imaged by the second optical component in the exit pupil. The first optical component includes a first optical element having a plurality of first raster elements that are imaged into the image plane producing a plurality of images being superimposed at least partially on a field in the image plane. The plurality of first raster elements have negative optical power.

[0001] The invention concerns an illumination system for wavelengths≦193nm as well as a projection exposure apparatus with such an illuminationsystem.

[0002] In order to be able to further reduce the structural widths ofelectronic components, particularly in the submicron range, it isnecessary to reduce the wavelengths of the light utilized formicrolithography. Lithography with very deep UV radiation, so called VUV(Very deep UV) lithography or with soft x-ray radiation, so called EUV(extreme UV) lithography, is conceivable at wavelengths smaller than 193nm, for example.

[0003] An illumination system for a lithographic device, which uses EUVradiation, has been made known from U.S. Pat. No. 5,339,346. For uniformillumination in the reticle plane and filling of the pupil, U.S. Pat.No. 5,339,346 proposes a condenser, which is constructed as a collectorlens and comprises at least 4 pairs of mirror facets, which are arrangedsymmetrically. A plasma light source is used as the light source.

[0004] In U.S. Pat. No. 5,737,137, an illumination system with a plasmalight source comprising a condenser mirror is shown, in which anillumination of a mask or a reticle to be illuminated is achieved bymeans of spherical mirrors.

[0005] U.S. Pat. No. 5,361,292 shows an illumination system, in which aplasma light source is provided, and the point plasma light source isimaged in an annular illuminated surface by means of a condenser, whichhas five aspherical mirrors arranged off-center.

[0006] From U.S. Pat. No. 5,581,605, an illumination system has beenmade known, in which a photon beam is split into a multiple number ofsecondary light sources by means of a plate with concave rasterelements. In this way, a homogeneous or uniform illumination is achievedin the reticle plane. The imaging of the reticle on the wafer to beexposed is produced by means of a conventional reduction optics.

[0007] EP-A-0 939 341 shows an illumination system and exposureapparatus for illuminating a surface over an illumination field havingan arcuate shape with x-ray wave length light. The illumination systemcomprises first and second optical integrators each with a plurality ofreflecting elements. The first and second optical integrators beingopposingly arranged such that a plurality of light source images areformed at the plurality of reflecting elements of the second opticalintegrator. To form an arcuate shaped illumination field in the fieldplane according to EP-A-0 939 341 the reflecting elements of the firstoptical integrator have an arcuate shape similar to the arcuateillumination field. Such reflecting elements are complicate tomanufacture.

[0008] EP-A-1 026 547 also shows an illumination system with two opticalintegrators. Similar to the system of EP-A-0 939 341 reflecting elementsof the first optical integrator have an arcuate shape for forming anarcuate shaped illumination field in the field plane.

[0009] In EP-A-0 955 641 a system with two optical integrators is shown.Each of said optical integrators comprises a plurality ofraster-elements. The raster elements of the first optical integrator areof rectangular shape. The arc-shaped field in the field plane is formedby at least one grazing incidence field mirror. Such systems are easierto manufacture than systems according to EP-A-0 939 341 or EP-A-1 026547.

[0010] The content of the above mentioned patent-applications areincorporated by reference.

[0011] All systems known from the state of the art, especially fromEP-A-0 939 341, EP-A-0 955 641 and EP-A-1 026 547 have the disadvantagethat the track lenght of the overall system is large.

[0012] It is therefore an object of the invention to ovcercome thedisadvantages of the illumination systems according to the state of artand to provide an illumination system for microlithography that fulfillsthe requirements for advanced lithography with wavelength less or equalto 193 nm. The illumination system should especially be compact in size.

[0013] The object of the invention is solved by an illumination systemwith the features of claim 1 and a projection exposure apparatus withthe features of claim 20.

[0014] The system illuminates a structured reticle arranged in the imageplane of the illumination system, which will be imaged by a projectionobjective onto a light sensitive substrate. In scanner-type lithographysystems the reticle is illuminated with a rectangular or arc-shapedfield, wherein a pregiven uniformity of the scanning energy distributioninside the field is required, for example better than ±5%. The scanningenergy is defined as the line integral over the light intensity in thescanning direction. The shape of the field is dependent on the type ofprojection objective. All reflective projection objectives typicallyhave an arc-shaped field, which is given by a segment of an annulus. Afurther requirement is the illumination of the exit pupil of theillumination system, which is located at the entrance pupil of theprojection objective. A nearly field-independent illumination of theexit pupil is required.

[0015] Typical light sources for wavelengths between 100 nm and 200 nmare excimer lasers, for example an ArF-Laser for 193 nm, an F₂-Laser for157 nm, an Ar₂-Laser for 126 nm and an NeF-Laser for 109 nm. For systemsin this wavelength region refractive components of SiO₂, CaF₂, BaF₂ orother crystallites are used. Since the transmission of the opticalmaterials deteriorates with decreasing wavelength, the illuminationsystems are designed with a combination of refractive and reflectivecomponents. For wavelengths in the EUV wavelength region, between 10 nmand 20 nm, the projection exposure apparatus is designed asall-reflective. A typical EUV light source is aLaser-Produced-Plasma-source, a Pinch-Plasma-Source, a Wiggler-Source oran Undulator-Source.

[0016] The light of this primary light source is directed to a firstoptical element, wherein the first optical element is part of a firstoptical component. Preferably the first optical component comprises acollector unit. The collector unit collects the light of the primarylight source. The first optical element is organized as a plurality offirst raster elements and transforms, preferably together with thecollector unit, the primary light source into a plurality of secondarylight sources. Each first raster element corresponds to one secondarylight source and focuses an incoming ray bundle, defined by all raysintersecting the first raster element, to the corresponding secondarylight source. The secondary light sources are arranged in a pupil planeof the illumination system or nearby this plane. A field lens forming asecond optical component is arranged between the pupil plane and theimage plane of the illumination system to image the secondary lightsources into an exit pupil of the illumination system, which correspondsto the entrance pupil of a following projection objective.

[0017] The first raster elements are imaged into the image plane,wherein their images are at least partially superimposed on a field thatmust be illuminated. Therefore, they are known as field raster elementsor field honeycombs. If the light source is a point-like source, thesecondary light sources are also point-like. In this case the imaging ofeach of the field raster elements can be explained visually with theprinciple of a “camera obscura”, with the small hole of the cameraobscura at the position of each corresponding secondary light source,respectively.

[0018] To superimpose the images of the field raster elements in theimage plane of the illumination system the incoming ray bundles aredeflected by the field raster elements with first deflection angles,which are not equal for each of the field raster elements but at leastdifferent for two of the field raster elements. Therefore individualdeflection angles for the field raster elements are designed.

[0019] For each field raster element a plane of incidence is defined bythe incoming and deflected centroid ray selected from the incoming raybundle. Due to the individual deflection angles, at least two of theincidence planes are not parallel.

[0020] In advanced microlithography systems the light distribution inthe entrance pupil of a projection objective must fulfill specialrequirements such as having an overall shape or uniformity. Since thesecondary light sources are imaged into the exit pupil, theirarrangement in the pupil plane of the illumination system determines thelight distribution in the exit pupil. With the individual deflectionangles of the field raster elements a predetermined arrangement of thesecondary light sources can be achieved, independent of the directionsof the incoming ray bundles.

[0021] For reflective field raster elements the deflection angles aregenerated by the tilt angles of the field raster elements. The tilt axesand the tilt angles are determined by the directions of the incoming raybundles and the positions of the secondary light sources, to which thereflected ray bundles are directed.

[0022] For refractive field raster elements the deflection angles aregenerated by lenslets, which have a prismatic optical power. Therefractive field raster elements can be lenslets with an optical powerhaving a prismatic contribution or they can be a combination of a singleprism and a lenslet. The prismatic optical power is determined by thedirections of the incoming ray bundles and the positions of thecorresponding secondary light sources.

[0023] Given the individual deflection angles of the first rasterelements, the beam path to the plate with the raster elements can beeither convergent or divergent. The slope values of the field rasterelements at the centers of the field raster elements has then to besimilar to the slope values of a surface with negative power to reducethe convergence of the beam path, or with positive power to increase theconvergence of the beam path. Finally the field raster elements deflectthe incoming ray bundles to the corresponding secondary light sourceshaving predetermined positions depending on the illumination mode of theexit pupil.

[0024] The diameter of the beam path is preferably reduced after thecollector unit to arrange filters or transmission windows with a smallsize. This is possible by imaging the light source with the collectorunit to an intermediate image. The intermediate image is arrangedbetween the collector unit and the plate with the field raster elements.After the intermediate image of the light source, the beam pathdiverges. An additional mirror to condense the diverging rays is notnecessary due to the field raster elements having deflecting opticalpower

[0025] For contamination reasons there is a free working distancebetween the light source and the collector unit, which results inconsiderable diameters for the optical components of the collector unitand also for the light beam. Therefore the collector unit has positiveoptical power to generate a converging ray bundle to reduce the beamdiameter and the size of the plate with field raster elements. Theconvergence of the light rays can be reduced with the field rasterelements, if the deflection angles are designed to represent a negativeoptical power according to the invention. For the centroid raysimpinging on the centers of the field raster elements, the collectorunit and the plate with the field raster elements then form a telescopesystem. The collector unit has positive optical power to converge thecentroid rays towards the optical axis, wherein the field rasterelements reduce the converging angles of the centroid rays. With thistelescope system the track length of the illumination system accordingto the invention can be reduced.

[0026] Preferably, the field raster elements are tilted planar mirrorsor prisms with planar surfaces, which are much easier to produce and toqualify than curved surfaces. This is possible, if the collector unit isdesigned to image the primary light source into the pupil plane of theillumination system, which would result in one secondary light source,if the field raster elements were omitted. The plurality of secondarylight sources is generated by the plurality of field raster elements,which distribute the secondary light sources in the pupil planeaccording to their deflection angles. The positive optical power tofocus the incoming ray bundles to the secondary light sources iscompletely provided by the collector unit Therefore the optical distancebetween the image-side principal plane of the collector unit and theimage plane of the collector unit is nearly given by the sum of theoptical distance between the image-side principal plane of the collectorunit and the plate with the field raster elements, and the opticaldistance between the plate with the field raster elements and the pupilplane of the illumination system. Due to the planar surfaces, the fieldraster elements do not influence the imaging of the primary light sourceinto one secondary light source, except for the dividing of this onesecondary light source into a plurality of secondary light sources dueto the deflection angles. For point-like or spherical sources thecollector unit has ellipsoidal mirrors or conical lenses with a first orsecond focus, wherein the primary light source is arranged in the firstfocus, and the secondary light source is arranged in the second focus ofthe collector unit.

[0027] Since according to the invention the focusing power of thecollector unit is large and the primary light source is imaged in frontof the pupil plane, the field raster elements have negative opticalpower. The field raster elements with negative optical power are convexmirrors in case of reflective systems or lenslets comprising negativeoptical power in case of refractive system to generate the secondarylight sources in or nearby the pupil plane.

[0028] The field raster elements are preferably arranged in atwo-dimensional array on a plate without overlapping. For reflectivefield raster elements the plate can be a planar plate or a curved plate.To minimize the light losses between adjacent field raster elements theyare arranged only with intermediate spaces between them, which arenecessary for the mountings of the field raster elements. Preferably,the field raster elements are arranged in a plurality of rows having atleast one field raster element and being arranged among one another. Inthe rows the field raster elements are put together at the smaller sideof the field raster elements. At least two of these rows are displacedrelative to one another in the direction of the rows. In one embodimenteach row is displaced relative to the adjacent row by a fraction of alength of the field raster elements to achieve a regular distribution ofthe centers of the field raster elements. The fraction is dependent onthe side aspect ratio and is preferably equal to the square root of thelength of one field raster element. In another embodiment the rows aredisplaced in such a way that the field raster elements are illuminatedalmost completely.

[0029] Preferably, only these field raster elements are imaged into theimage plane, which is completely illuminated. This can be realized witha masking unit in front of the plate with the field raster elements, orwith an arrangement of the field raster elements wherein 90% of thefield raster elements are completely illuminated.

[0030] It is advantageous to insert a second optical element with secondraster elements in the light path after the first optical element withfirst raster elements, wherein one first raster element corresponds toone of the second raster elements. Therefore, the deflection angles ofthe first raster elements are designed to deflect the ray bundlesimpinging on the first raster elements to the corresponding secondraster elements.

[0031] The second raster elements are preferably arranged at thesecondary light sources and are designed to image together with thefield lens the first raster elements or field raster elements into theimage plane of the illumination system, wherein the images of the fieldraster elements are at least partially superimposed. The second rasterelements are called pupil raster elements or pupil honeycombs. To avoiddamaging the second raster elements due to the high intensity at thesecondary light sources, the second raster elements are preferablyarranged defocused of the secondary light sources, but in a range from 0mm to 10% of the distance between the first and second raster elements.

[0032] For extended secondary light sources the pupil raster elementspreferably have a positive optical power to image the correspondingfield raster elements, which are arranged optically conjugated to theimage plane. The pupil raster elements are concave mirrors or lensletswith positive optical power.

[0033] The pupil raster elements deflect incoming ray bundles impingingon the pupil raster elements with second deflection angles in such a waythat the images of the field raster elements in the image plane are atleast partially superimposed. This is the case if a ray intersecting thefield raster element and the corresponding pupil raster element in theircenters intersects the image plane in the center of the illuminatedfield or nearby the center. Each pair of a field raster element and acorresponding pupil raster element forms a light channel.

[0034] The second deflection angles are not equal for each pupil rasterelement. They are preferably individually adapted to the directions ofthe incoming ray bundles and the requirement to superimpose the imagesof the field raster elements at least partially in the image plane.

[0035] With the tilt axis and the tilt angle for a reflective pupilraster element or with the prismatic optical power for a refractivepupil raster element the second deflection angle can be individuallyadapted.

[0036] For point-like secondary light sources the pupil raster elementsonly have to deflect the incoming ray bundles without focusing the rays.Therefore the pupil raster elements are preferably designed as tiltedplanar mirrors or prisms.

[0037] If both, the field raster elements and the pupil raster elementsdeflect incoming ray bundles in predetermined directions, thetwo-dimensional arrangement of the field raster elements can be madedifferent from the two-dimensional arrangement of the pupil rasterelements. Wherein the arrangement of the field raster elements isadapted to the illuminated area on the plate with the field rasterelements, the arrangement of the pupil raster elements is determined bythe kind of illumination mode required in the exit pupil of theillumination system. So the images of the secondary light sources can bearranged in a circle, but also in an annulus to get an annularillumination mode or in four decentered segments to get a Quadrupolillumination mode. The aperture in the image plane of the illuminationsystem is approximately defined by the quotient of the half diameter ofthe exit pupil of the illumination system and the distance between theexit pupil and the image plane of the illumination system. Typicalapertures in the image plane of the illumination system are in the rangeof 0.02 and 0.1. By deflecting the incoming ray bundles with the fieldand pupil raster elements a continuous light path can be achieved. It isalso possible to assign each field raster element to any of the pupilraster elements. Therefore the light channels can be mixed to minimizethe deflection angles or to redistribute the intensity distributionbetween the plate with the field raster elements and the plate with thepupil raster elements.

[0038] Imaging errors such as distortion introduced by the field lenscan be compensated for with the pupil raster elements being arranged ator nearby the secondary light sources. Therefore the distances betweenthe pupil raster elements are preferably irregular. The distortion dueto tilted field mirrors for example is compensated for by increasing thedistances between the pupil raster elements in a direction perpendicularto the tilt axis of the field mirrors. Also, the pupil raster elementsare arranged on curved lines to compensate for the distortion due to afield mirror, which transforms the rectangular image field to a segmentof an annulus by conical reflection. By tilting the field rasterelements the secondary light sources can be positioned at or nearby thedistorted grid of the corresponding pupil raster elements.

[0039] For reflective field and pupil raster elements the beam path hasto be folded at the plate with the field raster elements and at theplate with the pupil raster elements to avoid vignetting. Typically, thefolding axes of both plates are parallel. Another requirement for thedesign of the illumination system is to minimize the incidence angles onthe reflective field and pupil raster elements. Therefore the foldingangles have to be as small as possible. This can be achieved if theextent of the plate with the field raster elements is approximatelyequal to the extent of the plate with the pupil raster elements in adirection perpendicular to the direction of the folding axes, or if itdiffers less than ±10%.

[0040] Since the secondary light sources are imaged into the exit pupilof the illumination system, their arrangement determines theillumination mode of the pupil illumination. Typically the overall shapeof the illumination in the exit pupil is circular and the diameter ofthe illuminated region is in the order of 60%-80% of the diameter of theentrance pupil of the projection objective. The diameters of the exitpupil of the illumination system and the entrance pupil of theprojection objective are in another embodiment preferably equal. In sucha system the illumination mode can be changed in a wide range byinserting masking blades at the plane with the secondary light sourcesto get a conventional, Dipol or Quadrupol illumination of the exitpupil.

[0041] All-reflective projection objectives used in the EUV wavelengthregion have typically an object field being a segment of an annulus.Therefore the field in the image plane of the illumination system inwhich the images of the field raster elements are at least partiallysuperimposed has preferably the same shape. The shape of the illuminatedfield can be generated by the optical design of the components or bymasking blades which have to be added nearby the image plane or in aplane conjugated to the image plane.

[0042] The field raster elements are preferably rectangular. Rectangularfield raster elements have the advantage that they can be arranged inrows being displaced against each other. Depending on the field to beilluminated they have a side aspect ratio in the range of 5:1 and 20:1.The length of the rectangular field raster elements is typically between15 mm and 50 mm, the width is between 1 mm and 4 mm.

[0043] To illuminate an arc-shaped field in the image plane withrectangular field raster elements the field lens preferably comprises afirst field mirror for transforming the rectangular images of therectangular field raster elements to arc-shaped images. The arc lengthis typically in the range of 80 mm to 105 mm, the radial width in therange of 5 mm to 9 mm. The transformation of the rectangular images ofthe rectangular field raster elements can be done by conical reflectionwith the first field mirror being a grazing incidence mirror withnegative optical power. In other words, the imaging of the field rasterelements is distorted to get the arc-shaped images, wherein the radiusof the arc is determined by the shape of the object field of theprojection objective. The first field mirror is preferably arranged infront of the image plane of the illumination system, wherein thereshould be a free working distance. For a configuration with a reflectivereticle the free working distance has to be adapted to the fact that therays traveling from the reticle to the projection objective are notvignetted by the first field mirror.

[0044] The surface of the first field mirror is preferably an off-axissegment of a rotational symmetric reflective surface, which can bedesigned aspherical or spherical. The axis of symmetry of the supportingsurface goes through the vertex of the surface. Therefore a segmentaround the vertex is called on-axis, wherein each segment of thesurfaces which does not include the vertex is called off-axis. Thesupporting surface can be manufactured more easily due to the rotationalsymmetry. After producing the supporting surface the segment can be cutout with well-known techniques.

[0045] The surface of the first field mirror can also be designed as anon-axis segment of a toroidal reflective surface. Therefore the surfacehas to be processed locally, but has the advantage that the surroundingshape can be produced before surface treatment.

[0046] The incidence angles of the incoming rays with respect to thesurface normals at the points of incidence of the incoming rays on thefirst field mirror are preferably greater than 70°, which results in areflectivity of the first field mirror of more than 80%.

[0047] The field lens comprises preferably a second field mirror withpositive optical power. The first and second field mirror together imagethe secondary light sources or the pupil plane respectively into theexit pupil of the illumination system, which is defined by the entrancepupil of the projection objective. The second field mirror is arrangedbetween the plane with the secondary light sources and the first fieldmirror.

[0048] The second field mirror is preferably an off-axis segment of arotational symmetric reflective surface, which can be designedaspherical or spherical, or an on-axis segment of a toroidal reflectivesurface.

[0049] The incidence angles of the incoming rays with respect to thesurface normals at the points of incidence of the incoming rays on thesecond field mirror are preferably lower than 25°. Since the mirrorshave to be coated with multilayers for the EUV wavelength region, thedivergence and the incidence angles of the incoming rays are preferablyas low as possible to increase the reflectivity, which should be betterthan 65%. With the second field mirror being arranged as a normalincidence mirror the beam path is folded and the illumination system canbe made more compact.

[0050] By definition all rays intersecting the field in the image planehave to go through the exit pupil of the illumination system. Theposition of the field and the position of the exit pupil are defined bythe object field and the entrance pupil of the projection objective. Forsome projection objectives being centered systems the object field isarranged off-axis of an optical axis, wherein the entrance pupil isarranged on-axis in a finite distance to the object plane. For theseprojection objectives an angle between a straight line from the centerof the object field to the center of the entrance pupil and the surfacenormal of the object plane can be defined. This angle is in the range of3° to 10° for EUV projection objectives. Therefore the components of theillumination system have to be configured and arranged in such a waythat all rays intersecting the object field of the projection objectiveare going through the entrance pupil of the projection objective beingdecentered to the object field. For projection exposure apparatus with areflective reticle all rays intersecting the reticle needs to haveincidence angles greater than 0° to avoid vignetting of the reflectedrays at components of the illumination system.

[0051] In the EUV wavelength region all components are reflectivecomponents, which are arranged preferably in such a way, that allincidence angles on the components are lower than 25° or greater than65°. Therefore polarization effects arising for incidence angles aroundan angle of 45° are minimized. Since grazing incidence mirrors have areflectivity greater than 80%, they are preferable in the optical designin comparison to normal incidence mirrors with a reflectivity greaterthan 65%.

[0052] The illumination system is typically arranged in a mechanicalbox. By folding the beam path with mirrors the overall size of the boxcan be reduced. This box preferably does not interfere with the imageplane, in which the reticle and the reticle supporting system arearranged. Therefore it is advantageous to arrange and tilt thereflective components in such a way that all components are completelyarranged on one side of the reticle. This can be achieved if the fieldlens comprises only an even number of normal incidence mirrors.

[0053] The illumination system as described before can be usedpreferably in a projection exposure apparatus comprising theillumination system, a reticle arranged in the image plane of theillumination system and a projection objective to image the reticle ontoa wafer arranged in the image plane of the projection objective. Both,reticle and wafer are arranged on a support unit, which allows theexchange or scan of the reticle or wafer.

[0054] The projection objective can be a catadioptric lens, as knownfrom U.S. Pat. No. 5,402,267 for wavelengths in the range between 100 nmand 200 nm. These systems have typically a transmission reticle.

[0055] For the EUV wavelength range the projection objectives arepreferably all-reflective systems with four to eight mirrors as knownfor example from U.S. Ser. No. 09/503,640 showing a six mirrorprojection lens. These systems have typically a reflective reticle.

[0056] For systems with a reflective reticle the illumination beam pathbetween the light source and the reticle and the projection beam pathbetween the reticle and the wafer preferably interfere only nearby thereticle, where the incoming and reflected rays for adjacent objectpoints are traveling in the same region. If there are no furthercrossing of the illumination and projection beam path it is possible toseparate the illumination system and the projection objective except forthe reticle region.

[0057] The projection objective has preferably a projection beam pathbetween said reticle and the first imaging element which is tiltedtoward the optical axis of the projection objective. Especially for aprojection exposure apparatus with a reflective reticle the separationof the illumination system and the projection objective is easier toachieve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The invention will be described below on the basis of drawings.

[0059] Here:

[0060]FIG. 1: A schematic view of a refractive embodiment with prisms asfield raster, elements.

[0061]FIG. 2: A schematic view of a refractive embodiment according tothe invention with field raster elements having negative and prismaticoptical power.

[0062]FIG. 3: A schematic view of a reflective embodiment with convexmirrors as field raster elements and planar mirrors as pupil rasterelements.

[0063]FIG. 4: A schematic view of a reflective embodiment with convexmirrors as field raster elements and concave mirrors as pupil rasterelements.

[0064]FIG. 5: A schematic view of the principal setup of theillumination system.

[0065]FIG. 6: An Arrangement of the field raster elements.

[0066]FIG. 7: An Arrangement of the pupil raster elements.

[0067]FIG. 8: A schematic view of a reflective embodiment with a concavepupil-imaging field mirror and a convex field-forming field mirror.

[0068]FIG. 9: A schematic view of a reflective embodiment with a fieldlens comprising a telescope system and a convex field-forming fieldmirror.

[0069]FIG. 10: A detailed view of the embodiment of FIG. 9.

[0070]FIG. 11: Intensity distribution in the image plane of theembodiment of FIG. 10.

[0071]FIG. 12: Illumination of the exit pupil of the illumination systemof the embodiment of FIG. 10.

[0072]FIG. 13: A detailed view of a projection exposure apparatus.

[0073] To generally explain the effect of prismatic first rasterelements FIG. 1 depicts a purely refractive system in a schematicallyview. The beam cone of the light source 6501 is collected by theaspherical collector lens 6503 and is directed to the plate with thefield raster elements 6509. The collector lens 6503 is designed togenerate an image 6505 of the light source 6501 at the plate with thepupil raster elements 6515 as shown with the dashed lines if the platewith the field raster elements 6509 is not in the beam path. Thereforewithout the plate with the field raster elements 6509 one secondarylight source 6505 would be produced at the plate with the pupil rasterelements. This imaginary secondary light source 6505 is divided into aplurality of secondary light sources 6507 by the field raster elements6509 formed as field prisms 6511. The arrangement of the secondary lightsources 6507 at the plate with the pupil raster elements 6515 isproduced by the deflection angles of the field prisms 6511. These fieldprisms 6511 have rectangular surfaces and generate rectangular lightbundles. However, they can have any other shape. The pupil rasterelements 6515 are arranged nearby each of the secondary light sources6507 to image the corresponding field raster elements 6509 into thereticle plane 6529 and to superimpose the rectangular images of thefield raster elements 6509 in the field 6531 to be illuminated. Thepupil raster elements 6515 are designed as combinations of a pupil prism6517 and a pupil lenslet 6519 with positive optical power. The pupilprisms 6517 deflect the incoming ray bundles to superimpose the imagesof the field raster elements 6509 in the reticle plane 6529. The pupillenslets 6519 are designed together with the field lens 6521 to imagethe field raster elements 6509 into the reticle plane 6529. Thereforewith the prismatic deflection of the ray bundles at the field rasterelements 6509 and pupil raster elements 6515 an arbitrary assignmentbetween field raster elements 6509 and pupil raster elements 6515 ispossible. The pupil prisms 6517 and the pupil lenslets 6519 can also bemade integrally to form a pupil raster element 6515 with positive andprismatic optical power. The field lens 6521 images the secondary lightsources 6507 into the exit pupil 6533 of the illumination system formingtertiary light sources 6535 there.

[0074]FIG. 2 shows an inventive embodiment for a purely refractivesystem with first raster elements having negative optical power in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 1 increased by 200. Therefore, the descriptionto these elements is found in the description to FIG. 1. The asphericcollector lens 6703 is designed to focus the light rays of the lightsource 6701 in a plane 6705 which is arranged between the plate with thefield raster elements 6709 and the plate with the pupil raster elements6715 as indicated by the dashed lines. Therefore the field rasterelements 6709 have negative optical power to produce the secondary lightsources 6707 at the plate with the pupil raster elements 6715. The fieldraster elements 6709 are designed as combinations of a field prism 6711and a field lenslet 6713. The field prisms 6711 deflect the incoming raybundles to the corresponding secondary light sources 6707. The fieldlenslets 6713 are designed to generate the secondary light sources 6707at the corresponding pupil raster elements 6715. The field prisms 6711and the field lenslets 6713 can also be made integrally to form fieldraster elements 6709 with negative and prismatic optical power.

[0075]FIG. 3 shows an embodiment for a purely reflective system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 2 increased by 300. Therefore, the descriptionto these elements is found in the description to FIG. 2. The beam coneof the light source 7001 is collected by the ellipsoidal collectormirror 7003 and is directed to the plate with the field raster elements7009. The collector mirror 7003 is designed to generate an image 7005 ofthe light source 7001 between the plate with the field raster elements7009 and the plate with the pupil raster elements 7015 if the plate withthe field raster elements 7009 would be a planar mirror as indicated bythe dashed lines. The convex field raster elements 7009 are designed togenerate point-like secondary light sources 7007 at the pupil rasterelements 7015, since the light source 7001 is also point-like. Thereforethe pupil raster elements 7015 are designed as planar mirrors. Since theintensity at the point-like secondary light sources 7007 is very high,the planar pupil raster elements 7015 can alternatively be arrangeddefocused from the secondary light sources 7007. The distance betweenthe secondary light sources 7007 and the pupil raster elements 7015should not exceed 20% of the distance between the field raster elementsand the pupil raster elements. The pupil raster elements 7015 are tiltedto superimpose the images of the field raster elements 7009 togetherwith the field lens 7021 formed as the field mirrors 7023 and 7027 inthe field 7031 to be illuminated. Both, the field raster elements 7009and the pupil raster elements 7015 are tilted. Therefore the assignmentbetween the field raster elements 7009 and pupil raster elements 7015 isdefined by the user. In the embodiment of FIG. 3 the field rasterelements 7009 at the center of the plate with the field raster elements7009 correspond to the pupil raster elements 7015 at the border of theplate with the pupil raster elements 7015 and vice versa. The tiltangles and the tilt axes of the field raster elements are determined bythe directions of the incoming ray bundles and by the positions of thecorresponding pupil raster elements 7015. Since for each field rasterelement 7009 the tilt angle and the tilt axis is different, also theplanes of incidence defined by the incoming and reflected centroid raysare not parallel. The tilt angles and the tilt axes of the pupil rasterelements 7015 are determined by the positions of the corresponding fieldraster elements 7009 and the requirement that the images of the fieldraster elements 7009 has to be superimposed in the field 7031 to beilluminated. The concave field mirror 7023 images the secondary lightsources 7007 into the exit pupil 7033 of the illumination system formingtertiary light sources 7035, wherein the convex field mirror 7027 beingarranged at grazing incidence transforms the rectangular images of therectangular field raster elements 7009 into arc-shaped images.

[0076]FIG. 4 shows another embodiment for a purely reflective system ina schematically view. Corresponding elements have the same referencenumbers as those in FIG. 3 increased by 100. Therefore, the descriptionto these elements is found in the description to FIG. 3. In thisembodiment the light source 7101 and therefore also the secondary lightsources 7107 are extended. The pupil raster elements 7115 are designedas concave mirrors to image the field raster elements 7109 into theimage plane 7129. It is also possible to arrange the pupil rasterelements 7115 not at the secondary light sources 7107, but defocused.The influence of the defocus on the imaging of the field raster elements7109 has to be considered in the optical power of the pupil rasterelements.

[0077]FIG. 5 shows in a schematic view the imaging of one field rasterelement 7209 into the reticle plane 7229 forming an image 7231 and theimaging of the corresponding secondary light source 7207 into the exitpupil 7233 of the illumination system forming a tertiary light source7235. Corresponding elements have the same reference numbers as those inFIG. 3 increased by 200. Therefore, the description to these elements isfound in the description to FIG. 3.

[0078] The field raster elements 7209 are rectangular and have a lengthX_(FRE) and a width Y_(FRE). All field raster elements 7209 are arrangedon a nearly circular plate with a diameter D_(FRE) They are imaged intothe image plane 7229 and superimposed on a field 7231 with a lengthX_(field) and a width Y_(field), wherein the maximum aperture in theimage plane 7229 is denoted by NA_(field). The field size corresponds tothe size of the object field of the projection objective, for which theillumination system is adapted to.

[0079] The plate with the pupil raster elements 7215 is arranged in adistance of Z₃ from the plate with the field raster elements 7209. Theshape of the pupil raster elements 7215 depends on the shape of thesecondary light sources 7207. For circular secondary light sources 7207the pupil raster elements 7215 are circular or hexagonal for a densepackaging of the pupil raster elements 7215. The diameter of the platewith the pupil raster elements 7215 is denoted by D_(PRE).

[0080] The pupil raster elements 7215 are imaged by the field lens 7221into the exit pupil 7233 having a diameter of D_(EP). The distancebetween the image plane 7229 of the illumination system and the exitpupil 7233 is denoted with Z_(EP). Since the exit pupil 7233 of theillumination system corresponds to the entrance pupil of the projectionobjective, the distance Z_(EP) and the diameter D_(EP) are predeterminedvalues. The entrance pupil of the projection objective is typicallyilluminated up to a user-defined filling ratio σ.

[0081] The data for a preliminary design of the illumination system canbe calculated with the equations and data given below. The values forthe parameters are typical for a EUV projection exposure apparatus. Butthere is no limitation to these values. Wherein the schematic design isshown for a refractive linear system it can be easily adapted forreflective systems by exchanging the lenses with mirrors.

[0082] The field 7231 to be illuminated is defined by a segment of anannulus. The Radius of the annulus is

[0083] R_(field)=138 mm.

[0084] The length and the width of the segment are

[0085] X_(field)=88 mm, Y_(field)=8 mm

[0086] Without the field-forming field mirror which transforms therectangular images of the field raster elements into arc-shaped imagesthe field to be illuminated is rectangular with the length and widthdefined by the segment of the annulus.

[0087] The distance from the image plane to the exit pupil is

[0088] Z_(EP)=1320 mm.

[0089] The object field of the projection-objective is an off-axisfield. The distance—between the center of the field and the optical axisof the projection objective is given by the radius R_(field). Thereforethe incidence angle of the centroid ray in the center of the field is6°.

[0090] The aperture at the image plane of the projection objective isNA_(wafer)=0.25. For a reduction projection objective with amagnification ratio of β_(proj)=−0.25 and a filling ratio of σ=0.8 theaperture at the image plane of the illumination system is${NA}_{field} = {{\sigma \cdot \frac{{NA}_{wafer}}{4}} = 0.05}$

[0091] D_(EP)=2 tan└arcsin(NA_(field))┘·Z_(EP)≈2NA_(EP)≈132 mm

[0092] The distance Z₃ between the field raster elements and the pupilraster elements is related to the distance Z_(EP) between the imageplane and the exit pupil by the depth magnification α:

[0093] Z_(EP)=α·Z₃

[0094] The size of the field raster elements is related to the fieldsize by the lateral magnification β_(field):

[0095] X_(field)=β_(field)·X_(FRE)

[0096] Y_(field)=β_(field)·Y_(FRE)

[0097] The diameter D_(PRE) of the plate with the pupil raster elementsand the diameter D_(EP) of the exit pupil are related by the lateralmagnification β_(pupil):

[0098] D_(EP)=β_(pupil)·D_(PRE)

[0099] The depth magnification a is defined by the product of thelateral magnifications β_(field) and β_(pupil):

[0100] α=β_(field)·β_(pupil)

[0101] The number of raster elements being superimposed at the field isset to 200.

[0102] With this high number of superimposed images the required fieldillumination uniformity can be achieved.

[0103] Another requirement is to minimize the incidence angles on thecomponents For a reflective system the beam path is bent at the platewith the field raster elements and at the plate with the pupil rasterelements. The bending angles and therefore the incidence angles areminimum for equal diameters of the two plates:

[0104] D_(PRE)=D_(FRE)${200 \cdot X_{PRE} \cdot Y_{PRE}} = {{200 \cdot \frac{X_{field} \cdot Y_{field}}{\beta_{field}^{2}}} = {\frac{D_{EP}^{2}}{\beta_{pupil}^{2}} = {\frac{\beta_{field}^{2}}{\alpha^{2}}D_{EP}^{2}}}}$

[0105] The distance Z₃ is set to Z₃=900 mm. This distance is acompromise between low incidence angles and a reduced overall length ofthe illumination system. $\alpha = {\frac{Z_{EP}}{Z_{3}} = 1.47}$

Therefore${\beta_{field}} \approx \sqrt[4]{\frac{200 \cdot X_{field} \cdot Y_{field}}{D_{EP}^{2}}\alpha^{2}} \approx 2.05$${\beta_{pupil}} \approx \frac{\alpha}{\beta_{field}} \approx 0.7$$D_{FRE} = {D_{PRE} = {{\frac{\beta_{field}}{\alpha}D_{EP}} \approx {200\quad {mm}}}}$$X_{FRE} = {\frac{X_{field}}{\beta_{field}} \approx {43\quad {mm}}}$$Y_{FRE} = {\frac{Y_{field}}{\beta_{field}} \approx {4\quad {mm}}}$

[0106] With these values the principal layout of the illumination systemis known.

[0107] In a next step the field raster elements 7309 have to bedistributed on the plate as shown in FIG. 6. The two-dimensionalarrangement of the field raster elements 7309 is optimized forefficiency. Therefore the distance between the field raster elements7309 is as small as possible. Field raster elements 7309, which are onlypartially illuminated, will lead to uniformity errors of the intensitydistribution in the image plane, especially in the case of a restrictednumber of field raster elements 7309. Therefore only these field rasterelements 7309 are imaged into the image plane which are illuminatedalmost completely. FIG. 6 shows a possible arrangement of 216 fieldraster elements 7309. The solid line 7339 represents the border of thecircular illumination of the plate with the field raster elements 7309.Therefore the filling efficiency is approximately 90%. The rectangularfield raster elements 7309 have a length X_(FRE)=46.0 mm and a widthY_(FRE)=2.8 mm. All field raster elements 7309 are inside the circle7339 with a diameter of 200 mm. The field raster elements 7309 arearranged in 69 rows 7341 being arranged one among-another. The fieldraster elements 7309 in the rows 7341 are attached at the smaller y-sideof the field raster elements 7309. The rows 7341 consist of one, two,three or four field raster elements 7309. Some rows 7341 are displacedrelative to the adjacent rows 7341 to distribute the field rasterelements 7309 inside the circle 7339. The distribution is symmetrical tothe y-axis.

[0108]FIG. 7 shows the arrangement of the pupil raster elements 7415.They are arranged on a distorted grid to compensate for distortionerrors of the field lens. If this distorted grid of pupil rasterelements 7415 is imaged into the exit pupil of the illumination systemby the field lens a undistorted regular grid of tertiary light sourceswill be generated. The pupil raster elements 7415 are arranged on curvedlines 7443 to compensate the distortion introduced by the field-formingfield mirror. The distance between adjacent pupil raster elements 7415is increased in y-direction to compensate the distortion introduced byfield mirrors being tilted about the x-axis. Therefore the pupil rasterelements 7415 are not arranged inside a circle. The size of the pupilraster elements 7415 depends on the source size or source etendue. Ifthe source etendue is much smaller than the required etendue in theimage plane, the secondary light sources will not fill the plate withthe pupil raster elements 7415 completely. In this case the pupil rasterelements 7415 need only to cover the area of the secondary light sourcesplus some overlay to compensate for source movements and imagingaberrations of the collector-field raster element unit. In FIG. 7circular pupil raster elements 7415 are shown.

[0109] Each field raster element 7309 correspond to one of the pupilraster elements 7415 according to a assignment table and is tilted todeflect an incoming ray bundle to the corresponding pupil raster element7415. A ray coming from the center of the light source and intersectingthe field raster element 7309 at its center is deflected to intersectthe center of the corresponding pupil raster element 7415. The tiltangle and tilt axis of the pupil raster element 7415 is designed todeflect this ray in such a way, that the ray intersects the field in itscenter.

[0110] The field lens images the plate with the pupil raster elementsinto the exit pupil and generates the arc-shaped field with the desiredradius R_(field). For R_(field)=138 mm, the field forming gracingincidence field mirror has only low negative optical power. The opticalpower of the field-forming field mirror has to be negative to get thecorrect orientation of the arc-shaped field. Since the magnificationratio of the field lens has to be positive, another field mirror withpositive-optical power-is-required. Wherein for apertures NA_(field)lower than 0.025 the field mirror with positive optical power can be agrazing incidence mirror, for higher apertures the field mirror withpositive optical power should be a normal incidence mirror.

[0111]FIG. 8 shows a schematic view of a embodiment comprising a lightsource 7501, a collector mirror 7503, a plate with the field rasterelements 7509, a plate with the pupil raster elements 7515, a field lens7521, a image plane 7529 and a exit pupil 7535. The field lens 7521 hasone normal-incidence mirror 7523 with positive optical power for pupilimaging and one grazing-incidence mirror 7527 with negative opticalpower for field shaping. Exemplary for the imaging of all secondarylight sources, the imaging of one secondary light source 7507 into theexit pupil 7533 forming a tertiary light source 7535 is shown. Theoptical axis 7545 of the illumination system is not a straight line butis defined by the connection lines between the single components beingintersected by the optical axis 7545 at the centers of the components.Therefore, the illumination system is a non-centered system having anoptical axis 7545 being bent at each component to get a beam path freeof vignetting. There is no common axis of symmetry for the opticalcomponents. Projection objectives for EUV exposure apparatus aretypically centered systems with a straight optical axis and with anoff-axis object field. The optical axis 7547 of the projection objectiveis shown as a dashed line. The distance between the center of the field7531 and the optical axis 7547 of the projection objective is equal tothe field radius R_(field). The pupil imaging field mirror 7523 and thefield-forming field mirror 7527 are designed as on-axis toroidalmirrors, which means that the optical axis 7545 paths through thevertices of the on-axis toroidal mirrors 7523 and 7527.

[0112] In another embodiment as shown in FIG. 9, a telescope objectivein the field lens 7621 comprising the field mirror 7623 with positiveoptical power, the field mirror 7625 with negative optical power and thefield mirror 7627 is applied to reduce the track length furthermore.Corresponding elements have the same reference numbers as those in FIG.8 increased by 100. Therefore, the description to these elements isfound in the description to FIG. 8. The field mirror 7625 and the fieldmirror 7623 of the telescope objective in FIG. 9 are formed as anoff-axis Cassegrainian configuration. The telescope objective has anobject plane at the secondary light sources 7607 and an image plane atthe exit pupil 7633 of the illumination system. The pupil plane of thetelescope objective is arranged at the image plane 7629 of theillumination system. In this configuration, having five normal-incidencereflections at the mirrors 7603, 7609, 7615, 7625 and 7623 and onegrazing-incidence reflection at the mirror 7627, all mirrors arearranged below the image plane 7629 of the illumination system.Therefore, there is enough space to install the reticle and the reticlesupport system.

[0113] In FIG. 10 a detailed view of the embodiment of FIG. 9 is shown.Corresponding elements have the same reference numbers as those in FIG.9 increased by 100. Therefore, the description to these elements isfound in the description to FIG. 9. The components are shown in ay-z-sectional view, wherein for each component the local co-ordinatesystem with the y- and z-axis is shown. For the collector mirror 7703and the field mirrors 7723, 7725 and 7727 the local co-ordinate systemsare defined at the vertices of the mirrors. For the two plates with theraster elements the local co-ordinate systems are defined at the centersof the plates. In table 1 the arrangement of the local co-ordinatesystems with respect to the local co-ordinate system of the light source7701 is given. The tilt angles α, β and γ about the x-, y- and z-axisare defined in a right-handed system. TABLE 1 Co-ordinate systems ofvertices of mirrors X[mm] Y[mm] Z[mm] α[°] β[°] γ[°] Light source 77010.0 0.0 0.0 0.0 0.0 0.0 Collector mirror 0.0 0.0 125.0 0.0 0.0 0.0 7703Plate with field 0.0 0.0 −975.0 10.5 180.0 0.0 raster elements 7709Plate with pupil 0.0 −322.5 −134.8 13.5 0.0 180.0 raster elements 7715Field mirror 7725 0.0 508.4 −1836.1 −67.8 0.0 180.0 Field mirror 77230.0 204.8 −989.7 −19.7 0.0 180.0 Field mirror 7727 0.0 −163.2 −2106.249.4 180.0 0.0 Image plane 7731 0.0 −132.1 −1820.2 45.0 0.0 0.0 Exitpupil 7733 0.0 −1158.1 −989.4 45.0 0.0 0.0

[0114] The surface data are given in table 2. The radius R and theconical constant K define the surface shape of the mirrors according tothe formula${z = \frac{\frac{1}{R}h^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)\left( \frac{1}{R} \right)^{2}h^{2}}}}},$

[0115] wherein h is the radial distance of a surface point from thez-axis. TABLE 2 Optical data of the components Field Pupil Collectorraster raster Field Field Field mirror element element mirror mirrormirror 7703 7709 7715 7725 7723 7727 R [mm] −232.88 3600 −1239.7 −534.7−937.7 −65.5 K −0.74479 0.0 0.0 −0.0435 −0.0378 −1.1186 Focal - 1800617.6 −279.4 477.0 −757.1 length f [mm]

[0116] The light source 7701 in this embodiment is aLaser-Produced-Plasma source having a diameter of approximately 0.3 mmgenerating a beam cone with an opening angle of 83°. To decrease thecontamination of the collector mirror 7703 by debris of the source 7701the distance to the collector mirror 7703 is set to 125 mm.

[0117] The-collector mirror 7703 is an elliptical mirror, wherein thelight source 7701 is arranged in the first focal point of the ellipsoid.According to the invention the focusing power of the collector unit islarge and the primary light source is imaged in front of the pupilplane, if the field raster elements are planar. To generate secondarylight sources 7707 in or nearby the pupil plane the field rasterelements 7709 have to be convex mirrors. The distance between the vertexof the collector mirror 7703 and the center of the plate with the fieldraster elements 7709 is 1110 mm. The field raster elements 7709 arerectangular with a length X_(FRE)=46.0 mm and a width Y_(FRE)=2.8 mm.The arrangement of the field raster elements is shown in FIG. 6. Thetilt angles and tilt axis are different for each field raster element7709, wherein the field raster elements are tilted to direct theincoming ray bundles to the corresponding pupil raster elements 7715.The tilt angles are in the range of −4° to 4°. The mean incidence angleof the rays on the field raster elements is 10.5°. Therefore the fieldraster elements 7709 are used at normal incidence.

[0118] The plate with the pupil raster elements 7715 is arranged in adistance of 900 mm from the plate with the field raster elements 7709.The pupil raster elements 7715 are concave mirrors. The arrangement ofthe pupil raster elements 7715 is shown in FIG. 7. The tilt angles andtilt axis are different for each pupil raster element 7715, wherein thepupil raster elements 7715 are tilted to superimpose the images of thefield raster elements 7709 in the image plane 7731. The tilt angles arein the range of −4° to 4°. The mean incidence angle of the rays on thepupil raster elements 7715 is 7.5°. Therefore the pupil raster elements7715 are used at normal incidence.

[0119] The field mirror 7725 is a convex mirror. The used area of thismirror defined by the incoming rays is an off-axis segment of arotational symmetric conic surface. The mirror surface is drawn in FIG.10 from the vertex up to the used area as dashed line. The distancebetween the center of the plate with the pupil raster elements 7715 andthe center of the used area on the field mirror 7725 is 1400 mm. Themean incidence angle of the rays on the field mirror 7725 is 12°.Therefore the field mirror 7725 is used at normal incidence.

[0120] The field mirror 7723 is a concave mirror. The used area of thismirror defined by the incoming rays is an off-axis segment of arotational symmetric conical surface. The mirror surface is drawn inFIG. 10 from the vertex up to the used area as dashed line. The distancebetween the center of the used area on the field mirror 7725 and thecenter of the used area on the field mirror 7723 is 600 mm. The meanincidence angle of the rays on the field mirror 7723 is 7.5°. Thereforethe field mirror 7723 is used at normal incidence.

[0121] The field mirror 7727 is a convex mirror. The used area of thismirror defined by the incoming rays is an off-axis segment of arotational symmetric conic surface. The mirror surface is drawn in FIG.10 from the vertex up to the used area as dashed line. The distancebetween the center of the used area on the field mirror 7723 and thecenter of the used area on the field mirror 7727 is 600 mm. The meanincidence angle of the rays on the field mirror 7727 is 78°. Thereforethe field mirror 7727 is used at grazing incidence. The distance betweenthe field mirror 7727 and the image plane 7731 is 300 mm.

[0122] In another embodiment the field mirror and the field mirror arereplaced with on-axis toroidal mirrors. The vertices of these mirrorsare arranged in the centers of the used areas. The convex field mirrorhas a radius R_(y)=571.3 mm in the y-z-section and a radius R_(x)=546.6mm in the x-z-section. This mirror is tilted about the local x-axisabout 12° to the local optical axis 7745 defined as the connection linesbetween the centers of the used areas of the mirrors. The concave fieldmirror has a radius R_(y)=−962. 14 mm in the y-z-section and a radiusR_(x)=−945.75 mm in the x-z-section. This mirror is tilted about thelocal x-axis about 7.5° to the local optical axis 7745.

[0123]FIG. 11 shows the illuminated arc-shaped area in the image plane7731 of the illumination system presented in FIG. 10. The orientation ofthe y-axis is defined in FIG. 10. The solid line 7849 represents the50%-value of the intensity distribution, the dashed line 7851 the10%-value. The width of the illuminated area in y-direction is constantover the field. The intensity distribution is the result of a simulationdone with the optical system given in table 1 and table 2.

[0124]FIG. 12 shows the illumination of the exit pupil 7733 for anobject point in the center (x=0 mm; y=0 mm) of the illuminated field inthe image plane 7731. The arrangement of the tertiary light sources 7935corresponds to the arrangement of the pupil raster elements 7715, whichis presented in FIG. 7. Wherein the pupil raster elements in FIG. 7 arearranged on a distorted grid, the tertiary light sources 7935 arearranged on a undistorted regular grid. It is obvious in FIG. 12, thatthe distortion errors of the imaging of the secondary light sources dueto the tilted field mirrors and the field-shaping field mirror arecompensated. The shape of the tertiary light sources 7935 is notcircular, since the light distribution in the exit pupil 7733 is theresult of a simulation with a Laser-Plasma-Source which was notspherical but ellipsoidal. The source ellipsoid was oriented in thedirection of the local optical axis. Therefore also the tertiary lightsources are not circular, but elliptical. Due to the mixing of the lightchannels and the user-defined assignment between the field rasterelements and the pupil raster elements, the orientation of the tertiarylight sources 7935 is different for nearby each tertiary light source7935. Therefore, the planes of incidence of at least two field rasterelements have to intersect each other. The plane of incidence of a fieldraster element is defined by the centroid ray of the incoming bundle andits corresponding deflected ray.

[0125]FIG. 13 shows an EUV projection exposure apparatus in a detailedview. The illumination system is the same as shown in detail in FIG. 10.Corresponding elements have the same reference numbers as those in FIG.10 increased by 700. Therefore, the description to these elements isfound in the description to FIG. 10. In the image plane 8429 of theillumination system the reticle 8467 is arranged. The reticle 8467 ispositioned by a support system 8469. The projection objective 8471having six mirrors images the reticle 8467 onto the wafer 8473 which isalso positioned by a support system 8475. The mirrors of the projectionobjective 8471 are centered on a common straight optical axis 8447. Thearc-shaped object field is arranged off-axis. The direction of the beampath between the reticle 8467 and the first mirror 8477 of theprojection objective 8471 is tilted to the optical axis 8447 of theprojection objective 8471. The angles of the chief rays 8479 withrespect to the normal of the reticle 8467 are between 5° and 7°. Asshown in FIG. 13 the illumination system 8479 is well separated from theprojection objective 8471. The illumination and the projection beam pathinterfere only nearby the reticle 8467. The beam path of theillumination system is folded with reflection angles lower than 25° orhigher than 75° in such a way that the components of the illuminationsystem are arranged between the plane 8481 with the reticle 8467 and theplane 8383 with the wafer 8473.

1. An illumination system, particularly for microlithography withwavelengths≦193 nm, comprising: a primary light source (6501, 6701,7001, 7101, 7501, 7601, 7701, 8401); a first optical component; a secondoptical component (6521, 6721, 7021, 7121, 7521, 7621, 7721, 8421); animage plane (6529, 6729, 7029, 7129, 7529, 7629, 7729, 8429); and anexit pupil (6533, 6733, 7033, 7133, 7533, 7633, 7733, 8433); whereinsaid first optical component transforms said primary light source (6501,6701, 7001, 7101, 7501, 7601, 7701, 8401) into a plurality of secondarylight sources that are imaged by said second optical component (6521,6721, 7021, 7121, 7521, 7621, 7721, 8421) in said exit pupil (6533,6733, 7033, 7133, 7533, 7633, 7733, 8433), wherein said first opticalcomponent includes a first optical element having a plurality of firstraster elements (6509, 6709, 7009, 7109, 7509, 7609, 7709, 8409) thatare imaged into said image plane (6529, 6729, 7029, 7129, 7529, 7629,7729, 8429) producing a plurality of images being superimposed at leastpartially on a field in said image plane, wherein said plurality offirst raster elements (6509, 6709, 7009, 7109, 7509, 7609, 7709, 8409)have negative optical power.
 2. The illumination system according toclaim 1, wherein said plurality of first raster elements (6509, 6709,7009, 7109, 7509, 7609, 7709, 8409) are convex mirrors.
 3. Theillumination system according to claim 1, wherein said plurality offirst raster elements (6509, 6709, 7009, 7109, 7509, 7609, 7709, 8409)are lenses, having a negative optical power.
 4. The illumination systemaccording to claim 1, wherein said first optical component comprises acollector (6503, 6703, 7003, 7103, 7503, 7603, 7703, 8403) unit forcollecting a plurality of rays generated by said primary light source(6501,6701, 7001, 7101, 7501, 7601, 7701, 8401) and for directing saidplurality of rays to said first optical element and wherein saidcollector (6503, 6703, 7003, 7103, 7503, 7603, 7703, 8403) unit haspositive optical power to generate a converging ray bundle between saidcollector unit and said first optical element.
 5. The illuminationsystem according to one of the claims 1 to 4, wherein said plurality offirst raster elements deflect a plurality of incoming ray bundles todeflect ray bundles with first deflection angles, and wherein at leasttwo of said first deflection angles are different from one another. 6.The illumination system according to claim 5, wherein said plurality ofincoming ray bundles has a plurality of incoming centroid rays, whereinsaid plurality of deflected ray bundles has a plurality of deflectedcentroid rays, wherein each one of said plurality of deflected centroidrays corresponds to one of said plurality of incoming centroid ray thusdefining a plurality of planes of incidence, and wherein at least two ofsaid plurality of planes of incidence intersect each other.
 7. Theillumination system according to one of the claims 5 to 6, wherein eachof said plurality of first raster elements (6509, 6709, 7009, 7109,7509, 7609, 7709, 8409) corresponds to one of said plurality ofsecondary light sources (6507, 6707, 7007, 7107, 7507, 7607, 7707, 8407)and wherein each of said plurality of first raster elements deflects anincoming ray bundle to one of said corresponding secondary light sources(6507, 6707, 7007, 7107, 7507, 7607, 7707, 8407).
 8. The illuminationsystem according to claim one of the claims 5 to 7, wherein saidplurality of first raster elements (6509, 6709, 7009, 7109, 7509, 7609,7709, 8409) are mirrors being tilted to generate said first deflectionangles.
 9. The illumination system according to one of the claims 5 to8, wherein said first raster elements (6509, 6709, 7009, 7109, 7509,7609, 7709, 8409) are lenses comprising a prismatic optical power togenerate said first deflection angles.
 10. The illumination systemaccording to one of the claims 5 to 9, wherein said first opticalcomponent further comprises a second optical element having a pluralityof second raster elements (6515, 6715, 7015, 7115, 7415, 7515, 7615,7715, 8415), wherein each of said plurality of first raster elements(6509, 6709, 7009, 7109, 7509, 7609, 7709, 8409) corresponds to one ofsaid plurality of second raster elements (6515, 6715, 7015, 7115, 7415,7515, 7615, 7715, 8415) and wherein said each of said plurality of firstraster elements (6509, 6709, 7009, 7109, 7509, 7609, 7709, 8409)deflects one of said plurality incoming ray bundles to saidcorresponding one of said plurality of second raster elements (6515,6715, 7015,7115, 7415, 7515, 7615, 7715, 8415).
 11. The illuminationsystem according to claim 10, wherein said plurality of second rasterelements (6515, 6715, 7015, 7115, 7415, 7515, 7615, 7715, 8415) and saidsecond optical component image said corresponding first raster elementsinto said image plane.
 12. The illumination system according to one ofthe claims 10 to 11, wherein said plurality of second raster elements(6515, 6715, 7015, 7115,7415, 7515, 7615, 7715, 8415) are concavemirrors.
 13. The illumination system according to one of the claims 10to 11, wherein said plurality of second raster elements (6515,6715,7015, 7115,7415, 7515, 7615, 7715, 8415) are lenses with positiveoptical power.
 14. The illumination system according to one of theclaims 10 to 13, wherein said plurality of second raster elements (6515,6715, 7015, 7115, 7415, 7515, 7615, 7715, 8415) deflects said pluralityof incoming ray bundles with second deflection angles to superimposesaid plurality of images at least partially on said field.
 15. Theillumination system according to one of the claims 10 to 14, whereinsaid plurality of second raster elements (6515, 6715, 7015, 7115, 7415,7515, 7615, 7715, 8415) are tilted concave mirrors.
 16. The illuminationsystem according to one of the claims 10 to 14, wherein said pluralityof second raster elements (6515, 6715, 7015, 7115, 7415, 7515, 7615,7715, 8415) are prisms.
 17. The illumination system according to one ofthe claims 10 to 14, wherein said plurality of second raster elements(6515, 6715, 7015, 7115, 7415, 7515, 7615, 7715, 8415) are lenses havinga prismatic optical power and a positive optical power.
 18. Theillumination system according to one of the claims 1 to 17, wherein saidfield is a segment of an annulus, wherein said first raster elements(6507, 6707, 7007, 7107, 7507, 7607, 7707, 8407) are rectangular, andwherein said second optical component comprises a first field mirror(6507, 6707, 7007, 7107, 7507, 7607, 7707, 8407) for shaping said fieldto said segment of said annulus.
 19. The illumination system accordingto the claim 18, wherein said first field mirror has negative opticalpower and wherein said second optical component comprises a second fieldmirror (7023, 7123, 7523, 7623, 7723, 8423) with positive optical power.20. A projection exposure apparatus for microlithography comprising: theillumination system of one of the claims 1 to 19; a reticle (8467) beinglocated at said image plane (8429); a light-sensitive object (8473) on asupport system (8475); and a projection objective (8447) to image saidreticle (8467) onto said light-sensitive object.